There is an actuator including a motor and a deceleration mechanism. In addition, in the deceleration mechanism, as a deceleration mechanism that can obtain a high speed reduction ratio, for example, there is a differential gear deceleration mechanism disclosed in Patent Literature 1.
The differential gear deceleration mechanism has an input shaft connected to an output shaft of a motor and rotated therewith, a wobbling crown gear having a central axis wobbling about a rotation axis of the input shaft through rotation of the input shaft, a stationary crown gear fixed to a casing surrounding the rotation axis and meshed with the wobbling crown gear, an pressing mechanism attached to the input shaft and configured to press the wobbling crown gear toward the stationary crown gear, an output shaft rotatably supported by the casing surrounding the rotation axis, and an elastically deformable spoke configured to connect the wobbling crown gear and the output shaft.
In the differential gear deceleration mechanism, the number of teeth of the wobbling crown gear is different from the number of teeth of the stationary crown gear. For this reason, even when the wobbling crown gear is pressed toward the stationary crown gear by the pressing mechanism, only some of teeth of the wobbling crown gear are meshed with the stationary crown gear, and a central axis of the wobbling crown gear is inclined with respect to the rotation axis. Accordingly, the wobbling crown gear wobbles about the rotation axis with rotation of the input shaft.
In the differential gear deceleration mechanism, for example, when the number of teeth of the stationary crown gear is N and the number of teeth of the wobbling crown gear is (N−1), a speed reduction ratio, which is a ratio (1/N) of a difference in the number of teeth (1) of the gears to the number of teeth (N) of the stationary crown gear is obtained. In this way, since the differential gear deceleration mechanism is compact and lightweight and still obtains a high speed reduction ratio, for example, the mechanism is widely used for a finger joint of a robot hand or the like.